Update:
Nothing's left. I was thinking too complicated.
Fetching or forwarding in the virtual SME isn't needed. The real server's gateway has to be changed to the bridged IP of the virtual server. If DHCP is used, this has to be switched to the virtual SME. And, of course, the real network adapter of the laptop has to be configured in the network range of the LAN. *NOT* by DHCP. Can be checked in WIN7 with the cmd and ipconfig.
This can be only a temporarily solution (for me). There are a lot of important things which are managed by the IPCop. Today is Thursday, our old ISP told us that we're back online latest on Monday.
The IPCop is still untouched, power it on, turning the gateway back to the IPCop, and we are back on track. Til the new ISP comes up...